Adjsutable wrenches have been used for many years to allow a single wrench to torque different size nuts and bolt heads without the need of a set of wrenches of different sizes. Most adjustable wrenches have previously been constructed with a handle end and a single open wrench end of an adjustable size such as disclosed by U.S. Pat. Nos. 1,561,812 While; 1,585,825 Bessolo; 1,781,994 Wilson, 2,814,226 Logczyc; 3,673,896 Vardaman; and 4,065,986 Meggs et al. Other adjustable wrenches have been of the double-ended open wrench type wherein the wrench has opposite ends that respectively support a pair of adjustable open end wrenches such as disclosed by U.S. Pat. Nos. 1,215,726 Skew and 1,444,907 Fisher.
Other adjustable wrenches have been of the double-ended box type to which the present invention relates. Such double-ended box wrenches have an elongated shape with a closed box wrench at each end such as disclosed by U.S. Pat. Nos. 592,199 Fletcher and 3,282,136 Maichen. In the Fletcher wrench, one of the adjustable box wrenches has a hexagonal shape of an adjustable size for torquing hexagonal nuts and bolts while the other box wrench has a square shape of an adjustable size for torquing square nuts and bolts. Adjustment is provided by rotation of a nut that is received by a threaded stem connected to movable jaws that are respectively associated with the hexagonal and square box wrenches. In the Maichen patent, both box wrenches are of a hexagonal shape with one having a greater size than the other. Adjustment of the Maichen wrench is provided by rotational adjustment of a disc that has diametrically opposite notches spaced at different distances so as to receive and appropriately position jaw members respectively associated with the large and small hexagonal box wrenches.
In addition to open end and closed box adjustable wrenches, the prior art also discloses combination open end and box end adjustable wrenches. Such combination adjustable wrenches have one end with an adjustable open end wrench and another end with an adjustable closed box wrench. Examples of such combination adjustable wrenches are disclosed by U.S. Pat. Nos. 4,151,763 and 4,325,275 of Colvin. Also, one embodiment of the previously mentioned U.S. Pat. No. 3,282,136 of Maichen also is of the adjustable combination type with an adjustable open wrench at one end and an adjustable closed box wrench at its other end.
In order to perform effectively, adjustable wrenches must have the capability of being adjustable to the required size without tolerance variations that permit a slight opening of the wrench upon the application of torque. Such a slight opening can cause the wrench to slip over the corners of the nut or bolt and thereby provide rounding that makes it increasingly difficult to subsequently apply torque. Also, to be effective, the end size of adjustable wrenches cannot be too large so as to prevent use thereof in confined spaces as is often necessary.